Method and apparatus for controlling FCC hydrotreating by near-infrared spectroscopy

ABSTRACT

On-line controlling of FCC hydrotreating is provided which uses near infrared (NIR) analysis to characterize cracking feed for parameters and the resulting characterization thereof. The NIR results can be used in FCC hydroteating software to control on-line unit yields and qualities.

TECHNICAL FIELD

This invention relates to controlling FCC hydrotreating by near infraredspectroscopy. More specifically, the present invention relates toon-line controlling FCC hydrotreating for producing lower molecularweight products from hydrocarbon feeds by NIR spectroscopy.

BACKGROUND OF THE INVENTION

Near IR spectroscopy has been used in the past to determine physicalproperties of petroleum hydrocarbon mixtures. This includes using theNIR results to control refinery processes including gasoline blendersand catalytic reforming units. It is a quick, non-destructive analyticaltechnique that is correlated to primary test methods using amultivariate regression analysis algorithm such as partial least squaresor multiple linear regression. It has been used in a laboratory topredict properties of refinery blender streams and finished gasoline anddiesel fuel.

Optimization, design and control of catalytic cracking process units allbenefit from kinetic models which describe the conversion of feeds toproducts. In order to properly describe the effects of changes in feedcomposition, such models require descriptions of the feed in terms ofconstituents which undergo similar chemical reactions in the crackingunit. For design and optimization studies, a protocol which involvesoff-line feed analysis taking weeks or even months to provide a feeddescription.

For modern refineries, the Fluid Catalytic Cracking Unit (FCCU) produces40 to 60+ % of the gasoline in the gasoline pool. In addition, the FCCUproduces a blendstock component for diesel manufacture. Air qualityregulations for these transportation fuels will require a furtherreduction in sulfur content as mandated by the Clean Air Act. For theFCCU process, there are two routes a refiner can utilize to furtherreduce the sulfur content of these transportation fuels. The first routeis via a hydrotreatment process on the feedstock to the FCCU. Thishydrotreatment process can by operational severity and design, remove asubstantial amount of the feed sulfur to produce a gasoline sulfurcontent of 100 ppmw or less. The second route a refiner can takeinvolves the use of a specialized catalyst or additive in the FCCUcirculating catalyst inventory that can catalytically remove sulfur fromthe FCCU product distributions. Refiners may elect to use this route forboth non-hydrotreated and/or hydrotreated FCCU feedstock derived fromvarious crude sources. In addition, if a refiner utilizes the firstroute for desired gasoline sulfur content, when the hydrotreater istaken out of service for an outage, this specialized catalyst oradditive can be utilized to minimize the increase of gasoline sulfurduring the outage period.

However, this practice requires detailed feed and product yield andanalytical data. Current analytical techniques require a long lead timeto generate the needed input to the model.

In the search for improved petroleum refining, we have developed on-linecontrolling of FCC hydrotreating with NIR spectroscopy. A Near IR (NIR)spectrophotometer can be used to collect spectra on Fluid CatalyticCracking (FCC) feedstocks and products. NIR measurement of feed andproducts from a Cat Feed Hydrotreater (CFH) enables this process tooptimize catalyst cycle life, maximize product upgrade value, controlenvironmental emissions and FCC gasoline sulfur.

Other objects and advantages of the present invention will becomeapparent to those skilled in the art upon a review of the followingdetailed description of the preferred embodiments and the accompanyingdrawings.

SUMMARY OF THE INVENTION

The CFH pretreats the FCC feedstock to remove process FCC contaminantssuch has sulfur, nitrogen and concarbon. In the process, the CFH addshydrogen to the FCC feed and saturates some of the aromatic components.This results in improved yield selectivity from the FCC unit and higherproduct value. Use of on-line NIR characterization of feed and productfrom the CFH will provide improved control and operation to targets tomaximize FCC profitability and ensure FCC environmental emissions andproduct specifications are maintained. The CFH cycle life can also bemore effectively managed to ensure feed to the CFH is controlled toachieve the desired catalyst cycle life. On-line monitoring of feedquality will also assist in pro-active trouble shooting to minimizeoperating problems from feed quality upsets.

This novel use of NIR is the ability to measure feed and products to andfrom CFH and FCC unit on-line to serve as a tool to optimizeperformance.

CFH Optimization provides a good use of on-line operating modes. Ofspecial interest is aromatic saturation. Several units will rely on aCFH to meet gasoline pool sulfur requirements. However, operating in anaromatic saturation mode represents and opportunity to maximize overallefficiency based upon the improvement in FCC yields. Accurate feed andproduct aromatics and sulfur data is needed on-line to know where tooperate on the aromatics equilibrium curve.

Use of NIR to measure feed and products to and from the CFH and FCC willnow enable the user to adjust the CFH operating conditions to maximizeFCC feed value and adjust FCC operating conditions to maximize FCCproduct value. This is consistent with the FCC RTO application with theadded advantage of being able to pro-actively adjust the FCC feed valuewith the CFH optimization.

The present invention provides a process for controlling on-line FCChydrotreating exhibiting absorption in the near infreared (NIR) region.The process steps include:

-   -   a) measuring absorbances using a spectrometer measuring        absorbances at wavelengths within the range of about 780-4000        nm, e.g., 780-2500 nm, and outputting an emitted signal        indicative of said absorbance;    -   b) subjecting the NIR spectrometer signal to a mathematical        treatment (e.g. derivative, smooth, baseline correction) of the        emitted signal.    -   c) processing the emitted signal or the mathematical treatment        using a defined model to determine the chemical or physical        properties of the hydrotreating and outputting a processed        signal; and    -   d) controlling on-line in response to the processed signal, at        least one parameter of the FCC hydrotreating.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an FCC unit comprising a reactor and ahydrotreater showing the control system of the present invention inplace for operating that FCC unit.

FIG. 2 is a Table which shows samples, including hydrotreater chargesand products and FCC feeds used to control on-line weight percents ofeach hydrocarbon class.

FIG. 3 is a plot that illustrates HDS vs. As mode differences.

FIG. 4 is a graph of a catalyst cycle life curve.

FIG. 5 is a graph of an FCC feed upset showing high SO_(x).

FIG. 6 is a table of a neural network for on-line control of SO_(X)emissions.

FIG. 7 is a graph of the use of NIR on FCC hydrotreating.

DETAILED DESCRIPTION OF THE INVENTION

Petroleum refining is a never-ending quest for higher throughputs,better yields, higher onstream factors, improved reliability, cheaperfeedstocks and cleaner fuels. At the heart of this effort is the fluidcatalytic cracking or FCC process. The FCC process is undergoing wavesof evolutionary change with improvements in feed injection, risertermination, catalyst stripping, spent catalyst distribution, crackingcatalyst and additive performance, emissions reduction and FCC naphthasulfur reduction technology.

When seeking to optimize the performance of the FCC unit, it is criticalto accurately define the operation as it exists before decisionsregarding significant process or equipment changes are finalized. Thisinvolves careful and precise measurement of FCC yields as well as keyprocess parameters including feed quality; feed rate, FCC operatingconditions and FCC product properties.

We use a Near IR (NIR) spectrophotometer to collect spectra on FluidCatalytic Cracking (FCC) feedstocks and products. Improved FCC kineticmodels and computer simulations have resulted in use of an optimizerprogram to select operating parameters of the FCC unit to maximizeprocessing against unit constraints. This is typically done off-lineusing a discrete set of data. NIR measurement of feed and productsenables this process to be done on-line allowing the process to operateat maximum efficiency.

FCC Process

Catalytic cracking is the backbone of many refineries. It converts heavyfeeds (600°-1050° F.) such as atmospheric gas oil, vacuum gas oil, cokergas oil, lube extracts, and slop streams, into lighter products such aslight gases, olefins, gasoline, distillate and coke, by catalyticallycracking large molecules into smaller molecules. Catalytic crackingoperates at low pressures (15 to 30 psig), in the absence of externallysupplied H₂, in contrast to hydrocracking, in which H₂ is added duringthe cracking step. Catalytic cracking is inherently safe as it operateswith very little oil actually in inventory during the cracking process.

FCC feedstocks include that fraction of crude oil which boils at 650° to1000° F., such fractions being relatively free of coke precursors andheavy metal contamination. Such feedstock, known as “vacuum gas oil”(VGO) is generally prepared from crude oil by distilling off thefractions boiling below 650° F. at atmospheric pressure and thenseparating by further vacuum distillation from the heavier fractions acut boiling between 650° F. and 900° to 1025° F. The fractions boilingabove 900° to 1025° F. are normally employed for a variety of otherpurposes, such as asphalt, residual fuel oil, #6 fuel oil, or marineBunker C fuel oil. However, some of these higher boiling cuts can beused as feedstocks in conjunction with FCC processes which utilizecarbo-metallic oils by Reduced Crude Conversion (RCC) using aprogressive flow type reactor having an elongated reaction chamber.

The FCC process may be controlled by selecting a feedstock of specifiedcharacteristics to the unit as well as controlling process parameters.

Varying process conditions can affect the product slate. Operating undermore severe cracking conditions by increasing process temperatures canprovide a gasoline product of higher octane rating, while increasingconversion can provide more olefins for alkylate production, as well asmore gasoline and potential alkylate. Catalytic cracking can also beaffected by inhibitors, which can be naturally present in the feed oradded separately. Generally, as boiling range of the feed increases, sodoes the concentration of inhibitors naturally therein. Inhibitioneffect can be temporary or permanent depending on the type of inhibitorpresent. Nitrogen inhibitors generally provide temporary effects whileheavy metals such as nickel, vanadium, iron, copper, etc., which canquantitatively transfer from the feed to the catalyst provide morepermanent inhibition. Metals poisoning results in higher dry gas yields,higher hydrogen factor, higher coke yields as a percent of conversion,and lower gasoline yields. Coke precursors such as asphaltenes tend tobreak down into coke during cracking which deposits on the catalyst,reducing its activity.

In catalytic cracking, an inventory of particulate catalyst iscontinuously cycled between a cracking reactor and a catalystregenerator. In the fluidized catalytic cracking (FCC) process,hydrocarbon feed contacts catalyst in a reactor at 425°-600° C., usually460°-560° C. The hydrocarbons crack, and deposit carbonaceoushydrocarbons or coke on the catalyst. The cracked products are separatedfrom the coked catalyst. The coked catalyst is stripped of volatiles,usually with steam, and is then regenerated. In the catalystregenerator, the coke is burned from the catalyst with oxygen-containinggas, usually air. Coke burns off, restoring catalyst activity andheating the catalyst to, e.g., 500°-900° C., usually 600°-750° C. Fluegas formed by burning coke in the regenerator is discharged into theatmosphere.

FIG. 1 is a schematic diagram of an FCC unit comprising a reactor and ahydrotreater showing the control system of the present invention inplace for operating that FCC unit.

FIG. 1 shows feed 20 is heated by fired heater 22 which is heated by gasburner 24, fuel to which is controlled by automatic valve 26. Justbefore the fuel enters the fired heater 22, a sample 30 is withdrawn andconducted by tubing into NIR unit 32. In an alternate embodiment (notshown), a fiber optic probe inserted directly into the feed line beforefired heater 22 can obviate the need for withdrawing sample.

NIR unit 32 can be located on-line and can include a sample conditioningmeans for controlling the temperature, and for extracting bubbles anddirt from the sample. The NIR unit also comprises a spectrometer meanswhich may be a spectrometer of the NIR, Fourier Transform Near Infrared(FTNIR), Fourier Transform Infrared (FTIR), or Infrared (IR) type,ruggedized for process service and operated in a temperature-controlled,explosion-proof cabinet. A photometer with present optical filtersmoving successively into position, can be used as a special type ofspectrometer.

NIR spectrometer 32 outputs a signal to computer 40 which preferablytakes a derivative of the signal from the spectrometer, and subjects itto a defined model to generate the properties of interest. The model isoptionally derived from signals obtained from NIR measurement ofcracking products.

In operation, the FCCU operates conventionally with feed being fired inheater 22 entering riser 50, together with catalyst descending throughthe catalyst return line 52 and entering riser 50. The vaporizedproducts ascend riser 50 and are recovered in the reactor by cyclone 54with product vapors 58 exiting to the main column for fractionation andrecovery of various products. Naphtha product can be recycled throughline 60. Spent catalyst descends from the reactor through lines 64 intothe regenerator 68 and contacts air to burn off carbon and produce fluegas which exits through flue cyclone 70 and flue gas line 72. Variousother components are shown, but not described. For example, computer 40controls catalyst cooler 76 through catalyst temperature line 78.Injection water line 80 is also shown.

Optionally or alternatively, a second sample taken from the reactorproduct vapors 58 can be input through line 74 to NIR 32, permitting thespectrometer to analyze the products so that computer 40 can compare thegroup type analysis of the products against the optimum products slatedesired for maximum economy.

EXAMPLE 1

Different feedstocks will result in different yields from the FCCprocess. If the unit is operating against a constraint, the process willneed to adjust to avoid exceeding an equipment limitation. Typicalprocess variables include feed rate, reactor temperature, feed preheatand pressure. The process response from each of the variables isnon-linear. The optimum set of conditions to maximize profitability tounit constraints will typically vary depending upon the feed quality.The following is an example of different operating conditions requiredto maximize profitability for a change in feed:

Nor- New Feed New Feed New Feed mal with Multi- with Only with OnlyOper- variable Rate ROT ation Optimization Varied Varied Feed PropertiesAPI 24.6 21.8 21.8 21.8 UOP K 11.69 11.77 11.77 11.77 Concarbon (%) 0.150.59 0.59 0.59 Nitrogen (ppm) 1150 162 162 162 Sulfur (%) 0.34 0.55 0.550.55 1-ring Aromatics (%) 35 29 29 29 2-ring Aromatics (%) 34 26 26 263-ring Aromatics (%) 17 25 25 25 4-ring Aromatics+(%) 14 20 20 20Process Conditions Feed Rate (% Capacity) 100 95.3 83.8 100 ReactorTemperature (F.) 1010 992 1006 986 Reactor Pressue (psig) 34.7 33.6 32.334.2 Equipment Constraints Wet Gas Compressor (%) 100 100 100 100 MainAir Blower (%) 100 90 84 94 Yields Conversion (lv %) 77.55 74.33 76.8373.59

The results show the application of RTO using NIR allows the FCC processto automatically adjust processing conditions to maximize processing asfeedstock quality changes. Without the feedstock quality via NIR andRTO, the process will operate at a non-optimum condition until a modeloptimizer can be run and the results implemented. Conventional practiceis limited to use of APC where typically only 1 variable an bemanipulated to push the unit against constraints. On-line RTO chooses aset of operating conditions to maximize value.

EXAMPLE 2

FIG. 2 is a Table which shows samples, including hydrotreater chargersand products and FCC feeds used to control weight percents of eachhydrocarbon class.

Two hundred fifty samples, including hydrotreater charges and productsand FCC feeds were used to create a PLS model for predicting weightpercents of each hydrocarbon class. The samples were analyzed using theonline NIR. Wavelengths were chosen for each group and a summary appearsin FIG. 2.

EXAMPLE 3

FIG. 3 is a plot that illustrates HDS vs. AS mode differences. The plotshows FCC feed sulfur under different operating philosophies. The feedsulfur is held constant and aromatics, nitrogen or concarbon parametersare varied.

EXAMPLE 4

FIG. 4 is a graph of a catalyst cycle life curve. A critical aspect ofmanaging the CFH is catalyst cycle life. Coke and metals are depositedon the catalyst during the course of the run cycle. This deactivationrequires an increase in temperature. End of Run is typically determinedwhen the process is at its maximum inlet temperature capability. At thispoint the catalyst will need to be changed out with fresh. Monitoringthe CFH feed properties will ensure the unit is managed to achieve thedesired cycle length and avoid an upset condition where poor feedquality is sent to the unit. This ability to monitor feed provides forgreater flexibility and minimizes risk for increased deactivation andcatalyst damage. FIG. 4 is a typical catalyst cycle life curve showingthe impact of a feed upset. In this case the upset was caused by aleaking heat exchanger. Application of the NIR for on-line feedmonitoring would allow better unit monitoring to minimize the risk ofthis type of upset.

EXAMPLE 5

FIG. 5 is a graph of an FCC feed upset showing high SO_(x). All FCCunits have environmental emission limits. These are typically SO_(x),NOx, CO and particulate matter. Advanced monitoring of FCC feedproperties for S and N will enable the refiner to adjust processconditions to ensure a feed change or upset will not cause anenvironmental exceedence. Operating actions may include decreasingfederate, changing feed line-ups, diverting certain feed streams, andadjusting catalyst additive use for Sox and NOx. FIG. 5 is an example ofan FCC feed upset resulting in high Sox and opacity. Use of NIR on theFCC feed stream would provide advance notice of the pending problem andenable the operator to take action to mitigate.

EXAMPLE 6

FIG. 6 is a table of a neural network for on-line control of SO_(x)emissions. The NIR analyzer on the FCC feed can also be used to modelFCC emissions. Several refiners have developed either statistical orneural network models to predict FCC emissions either with or withoutcatalyst additives. Use of the NIR to measure feed characterizationwould be an important new parameter to improve model accuracy. Currentmodels are developed based upon daily feed samples that often result inpoor correlations due to variability. FIG. 6 is a summary of a neuralnetwork model variables use to predict SO_(x) emissions on the FCC unitat a refinery. NIR would allow for improved monitoring of the Feedproperties and improve the model's capacity.

EXAMPLE 7

FIG. 7 is a graph of the use of NIR on FCC hydrotreating. Refiners havehad to choose between pre-treat and post-treat options to meet gasolinesulfur requirements. Units that rely on controlling FCC feed sulfur viapre-treating with a CFH will see variation in the feed sulfur togasoline sulfur ratio with different crude types, CFH operatingconditions and degree of hydroprocessing. In order to ensure gasolineproduct quality, it is important to ensure gasoline sulfur content iscontrolled. Use of NIR on the FCC feed would allow the unit to adjustprocessing conditions to maintain product quality and avoid an off-specproduct. On-line monitoring of FCC feed quality will allow the operatorto adjust the CFH severity, change FCC federate, divert certain feedstreams and adjust product fractionation to maintain product quality.FIG. 7 is a typical relationship between feed sulfur, gasoline sulfurand gasoline endpoint. The NIR capability would allow the process tostay at the control point of this curve.

EXAMPLE 8 (Troubleshooting)

FCC Troubleshooting—Use of an on-line NIR would aid in identifyingproblems with upstream units in advance of current monitoringtechniques. This advance notice will aid in pro-active troubleshootingto mitigate the detrimental effects. This may include the following:

a) High salt content indicating potential desalted problem or crudequality change (examples from Texas City sodium with High Island Crude).

b) High metals (Ni+V), co carbon and endpoint resulting from a HEX leakin the crude/vacuum unit or CFH.

c) High co carbon, endpoint and metals resulting from black oilentrainment due to a low wash rate or mechanical problems incrude/vacuum.

d) Poor quality due to stratified tanks or bad line-up from the tankfarm.

Modifications

Specific compositions, methods, or embodiments discussed are intended tobe only illustrative of the invention disclosed by this specification.Variation on these compositions, methods, or embodiments are readilyapparent to a person of skill in the art based upon the teachings ofthis specification and are therefore intended to be included as part ofthe inventions disclosed herein.

The above detailed description of the present invention is given forexplanatory purposes. It will be apparent to those skilled in the artthat numerous changes and modifications can be made without departingfrom the scope of the invention. Accordingly, the whole of the foregoingdescription is to be construed in an illustrative and not a limitativesense, the scope of the invention being defined solely by the appendedclaims.

1. A process for controlling on line FCC hydro treating (CFH) exhibitingabsorption in the near infrared (NIR) region comprising: a) measuringabsorbances using a NIR spectrometer measuring absorbance's atwavelengths within the range of about 780-4000 nm, and outputting anemitted signal indicative of said absorbance; b) subjecting the NIRspectrometer signal to a mathematical treatment (e.g. derivative,smooth, baseline correction) of the emitted signal; c) processing theemitted signal or the mathematical treatment using a defined model todetermine the chemical or physical properties of the hydro treating andoutputting a processed signal; and d) controlling on-line in response tothe processed signal, at least one parameter of the catalytic crackingfeed, intermediate or product.
 2. The process of claim 1 including thestep of using NIR measuring on line to control CFH pretreats of FCCfeeds.
 3. The process of claim 2 wherein CFH pretreats remove FCCprocessing contaminants.
 4. The process of claim 3 wherein thecontaminants are sulfur nitrogen or concarbon.
 5. The process of claim 1including the step of using NIR measuring on line to control CFHpretreats to control weight percents of each hydrocarbon class.
 6. Theprocess of claim 1 including the step of using NIR measuring on line tocontrol CFH pretreats to hold sulfur content constant and varyaromatics, nitrogen or concarbon parameters.
 7. The process of claim 1including the step of using NIR measuring on line to control CFHpretreats to provide real time optimization of FCC processing.
 8. Theprocess of claim 1 including the step of using NIR measuring on line tocontrol CFH pretreats to manage CFH catalyst life.
 9. The process ofclaim 1 including the step of using NIR measuring on line to control CFHpretreats to control SO_(x), NO_(x), Co or particulate matter in FCCprocessing.
 10. The process of claim 1 including the step of using NIRmeasuring on line to control CFH pretreats to adjust the CFH severity,change FCC federate, divert certain feed streams and adjust productfractionation to maintain product quality.
 11. The process of claim 1including the step of using NIR measuring on line to control CFHpretreats to control feed sulfur, gasoline sulfur or gasoline endpoint.12. The process of claim 1 including the step of using NIR measuring online to control CFH pretreats to troubleshoot FCC processing.
 13. Theprocess of claim 12 wherein the step of troubleshooting mitigatesdetrimental effects.
 14. The process of claim 13 wherein the detrimentaleffects are high salt content, high metals, or high deposits.
 15. Theprocess of claim 1 wherein said absorbances are measured at wavelengthswithin the range of about 780-2500 nm.
 16. The process of claim 1wherein said absorbances are measured at wavelengths within the range of1100-2200 nm.
 17. The process of claim 1 wherein said absorbance ismeasured in at least one wavelength and includes the steps of: a)periodically or continuously outputting a periodic or continuous signalindicative of the intensity of said absorbance in said wavelength, orwavelengths in said two or more bands or a combination of mathematicalfunctions thereof, b) mathematically converting the signal to an outputsignal indicative of the mathematical function; and  controlling thehydro treating on-line in response to the output signal.
 18. The processof claim 1 wherein the step of controlling on-line allows for real timeoptimization processing.
 19. The process of claim 1 including the stepof: mathematically converting the signal to an output signal indicativeof the parameter.
 20. The process of claim 6 including the steps of:periodically or continuously outputting a periodic or continuous signalindicative of the intensity of the NIR absorbance in the wavelength, orwavelengths in the two or more bands or a combination of mathematicalfunctions thereof, mathematically converting said signal to an outputsignal indicative of the mathematical function; and controlling on-linein response thereto.
 21. The process of claim 1 including the step ofusing the NIR results in FCC hydrotreating simulation software tocontrol on-line unit yields and qualities.
 22. The process of claim 1including the step of using NIR measuring on-line to control FCCpretreats to maximize aromatic saturation by varying temperature tooptimize feed upgrading to the FCC.